Platelet-derived growth factor (PDGF) is a potent mitogen to cells of mesenchymal origin. In order to elucidate the structure-function relationships between ligand-receptor and receptor-signaling molecules, the extracellular domains of the PDGF receptor, the intracellular tyrosine kinase and the Src-homology region 2 (SH2) of PI-3 kinase and GAP have been expressed. The proteins have been purified for structural and functional analysis. Currently, it has been shown that the N-SH2 domain of PI-3 kinase binds the alphaPDGFR through a calcium dependent mechanism (manuscript submitted to J Biol chem, 1993). further, a large proportion of the proteins expressed for both x-ray crystallography and nuclear magnetic resonance spectroscopy have been committed. Currently, the three-dimensional structure of keratinocyte growth factor (KGF) and a mutant of KGF are in the process of being analyzed. the molecules have been model built on a computer graphics system based on the three- dimensional structure of fibroblast growth factor (FGF).